Resistance to hyperosmotic stress in boar spermatozoa: the role of the ionic pumps and the relationship with cryosurvival

The resistance to changes in the osmolarity of boar sperm was used to measure the resistance of boar sperm cells against freezing/thawing. Semen was incubated for 5 min in different solutions ranging from about 600 mOsm to about 4000 mOsm, and at 4°C, 16°C or 37°C (undisturbed media). This undisturbed media was constituted by NaCl, glycerol or glucose. This semen was then placed in an isoosmotic solution (disrupted solutions). Incubation in undisturbed media did not alter the percentages of viability or altered acrosomes, except when the initial incubation has been at 37°C and with osmolarities above 1000 mOsm. Viability and altered acrosome statistics were strongly modified in disrupted media. These effects are dependent upon the initial osmolarity of the media, but not upon the temperature. Pre-incubation with ouabain or amiloride did not affect spermatozoa incubated at 16°C in a 2211 mOsm, NaCl medium. However, in sperm incubated in this 2211 mOsm medium, and then rapidly placed in an isoosmotic solution, ouabain induced a decrease in viability and an increase in altered acrosomes. Amiloride did not affect the response of cells to the disrupted medium. Some significant correlations were observed among the percentages of altered acrosomes after hyperosomotic stress and some quality parameters of the fresh boar semen, especially the motion parameters. Although the resistance to hyperosmotic stress could be a valuable parameter in assessing fresh semen quality analysis, its usefulness in frozen-thawed semen is compromised, since other factors beside osmotic changes are involved in the resistance of boar semen to freezing-thawing. The Na+K+, ouabain-dependent ATP-ase activity seems to be related to the mechanisms of resistance to hyperosmotic stress in boar sperm.